Many common chemicals that are used by dispersing or dissolving in water are initially produced and packaged In powdered form. Examples of water dispersed or dissolved chemicals are agricultural chemicals such as pesticides which are applied as a water spray, caustic cleaners and detergents, and process chemicals such as pigments, dyes and carbon black.
There are, however, several problems associated with the use of these products due to their toxicity or high concentration. Such problems include accidental exposure of the user or the immediate environment to the chemicals, accuracy in measurement during the addition of the chemical to water tanks, and, finally, the disposal of the package in which the chemicals were delivered.
For the above reasons there has been a keen interest in packaging water soluble or water dispersible chemicals In water soluble films. Such packages would have the following advantages: human contact with the concentrated chemical would be eliminated, accurate dosages of the chemicals would be assured, and the disposal problem would be eliminated.
While there are water soluble PVOH films available for packaging materials, such PVOH films typically lack the alkaline stability necessary for packaging alkaline, or caustic, compositions such as cleaning products and detergents. Typically, a partially hydrolyzed PVOH is used to produce the cold water soluble film for packaging the alkaline product. However, the partially hydrolyzed PVOH being in contact with the alkaline product will undergo further hydrolysis reaction to produce a fully hydrolyzed PVOH film.
This fully hydrolyzed film has two major drawbacks. First, due to an increase in the overall degree of hydrolysis of the PVOH, the film becomes cold water insoluble. Secondly, a fully hydrolyzed PVOH film is highly crystalline. This highly crystalline film is more brittle and subject to cracking at low humidity which may result in accidental spillage of the chemicals and contamination of both humans and the environment.
Many attempts have been reported to improve the pH stability of the PVOH films. These efforts have included the selection of a special plasticizer: U.S. Pat. No. 2,948,697; 3,106,543 and 3,157,611; or blending PVOH with an alkaline, stable water soluble polymer such as disclosed in U.S. Pat. No. 2,850,741; 3,695,989; 3,892,905; 4,481,326 and 4,692,494. Other approaches to producing a pH stable PVOH have been directed at the modification or copolymerization of polyvinyl alcohol as disclosed in U.S. Pat. No. 3,441,547; 3,505,303; 4,747,976 and 4,844,828.
U.S. Pat. No. 4,692,494 discloses water soluble films of polyvinyl alcohol and polyacrylic acid and packages comprising same.
In addition to PVOH films, there are alkaline water soluble, acid functional resins which Include copolymers of (meth)acrylates and (meth)acrylic acid offered by Belland AG under the trademark BELLAND 2620 and 2585. However, these films either lack tensile strength or are very brittle and crack at low temperatures and relative humidity.
EP 0 415 357 A discloses a method for producing thermoplastic PVOH compositions.